The present invention relates to a device for adjusting a fuel injector electromagnetic metering valve.
The metering valves of fuel injectors generally comprise a control chamber with a drain conduit normally closed by a shutter which, in known metering valves, is normally closed by the armature of an electromagnet, and is released to open the conduit by energizing the electromagnet so as to move the armature towards the core of the magnetic circuit of the electromagnet.
As is known, the main parameter for evaluating the efficiency of a metering valve is the maximum permissible operating frequency, which depends on the speed with which the valve responds to a command to open or close the drain conduit, and hence on the speed with which it responds to energizing or de-energizing of the electromagnet.
In known metering valves, when the electromagnet is energized, the armature is generally arrested directly on the core; and, when the electromagnet is de-energized, the armature, due to the residual magnetic field, tends to stick to the core so that, to ensure rapid response when closing the injector, a large size return spring is required, the force of which however must be overcome by the electromagnet when opening the valve.
In some known metering valves, the pole pieces of the core present a layer of nonmagnetic material for achieving a minimum gap between the core and armature and reducing the effect of the residual magnetic field of the core on the armature. In such valves, however, repeated impact of the armature on the protective coating of the core, which is made of sintered material, seriously reduces the working life of the protective layer and/or the core; while no provision is made for adjusting the gap.
Other known metering valves comprise a device for adjusting the stop position of the armature, and in turn comprising an adjusting screw housed in a threaded sleeve at the base of the injector body, and which provides for positioning an axial stop for a pin integral with the armature. This device, too, presents several drawbacks, in that it fails to provide for setting a predetermined displacement of the armature; and the adjusting screw, despite being fitted with a lock nut, tends to work loose, thus possibly resulting in the armature contacting the core.